Halakhah for Sukkah 90:15

That is that He commanded us to swear by His name when it is necessary to ratify something or to deny it. For there is aggrandizement, glory and exhalation through this. And that is His, may He be blessed, saying, "and by His name shall you swear" (Deuteronomy 10:20). And in the explanation, they said, "The Torah said, 'Swear,' and the Torah said, 'Do not swear' - meaning to say, just like it prohibits an oath for which there is no need, and it is a negative commandment; so too is there a commandment [to make] an oath when it is needed, and it is a positive commandment. And as a result, it is not permitted to swear by any of all the creatures, such as the angels or the stars, except by way of nullifying what is attached. This is like one who swears by the sun, but he means to say, the Master of the sun. And in this way, our nation swears by the name of our teacher, Moshe - how glorious is his name - as if the one swearing was swearing by the Master or by the One who sent him. But so long as the one who swears is not intending this, but is swearing by one of the creatures, to believe in it - that it has intrinsic truth, to the point that he swears by it - he has already transgressed and associated something else with the name of the Heavens. About this comes the explanation (Sukkah 45b), "Anyone who associates the name of the Heavens with something else is uprooted from the world." And this is matter that the verse, "and by His name shall you swear," intended - meaning that only about Him should you believe that there is truth by which it is appropriate to swear. And they already said at the beginning of Temurah (Temurah 3b), "From where [do we know] that we may swear to perform the commandments? As it is written, 'and by His name shall you swear.'" (See Parashat Ekev; Mishneh Torah, Oaths 11.)